Black Orcs are not subject to animosity like their lesser brethren. The are also 'armed to da teeth' which means they can elect to fight with 2 choppas (2 attacks str 5 in first round), a single choppa and shield (1 attack at str 5, +1 armour save) or a great weapon (str 6 attack, no shield).
Furthermore, Black Orcs are quite a bit harder than normal Orcs with +1 Ws, +1 str and +1 leadership.
Are you beginning to see my point ?
Just being immune to animosity means that you retain a greater degree of control over your army because the black orcs will not squabble against one another and help to quell trouble in the ranks if you make them unit leaders of normal orcs.
At 11 points (if you excluded their heavy armour) they are more than twice the cost of a normal orc but 2 str 5 attacks in the 1st round of combat is something you might not want to miss out on.
One other thing... Have you heard of Grimgor Ironhide ? He is a must have, cheap and extremely hard Black Orc (infact pound for pound he's one of the hardest characters in the game - and a lot harder than 'Pretty Boy' Floyd Mayweather !
Take at least one special unit of Black Orcs just to accompany Grimgor into battle. You won't live to regret it and neither will your enemy... Live that is !
